An optical unit in which imaging optical members for taking an observation image or illumination optical members for emitting illumination light are housed in a cylindrical member is provided in a tip portion of an endoscope insertion unit, to be inserted into a subject body, of endoscope apparatus. With the recent miniaturization and increase in the number of recording pixels of solid-state imaging devices, the accuracy (working errors and assembling errors) that is required in attaching such an optical unit to the tip portion of an endoscope insertion unit has become higher. This is because an image failure such as a half blur or an illumination failure may occur if the optical unit is placed in the tip portion of the endoscope insertion unit at a position that is deviated from a regular position.
In view of the above, a technique has been proposed in which the optical axis of the optical unit is deviated from the center line of the outer circumferential surface of the cylindrical member of the optical unit and the position of the optical axis is fine-adjusted with respect to the tip portion of the endoscope insertion unit by rotating the optical unit in attaching it to the tip portion of the endoscope insertion unit (refer to JP-A-2008-257243, for example).